IBAN: Difference between revisions

This program uses the Maybe and Either monads to handle failures. Values of type 'Maybe a' can contain 'Nothing' (no value) or 'Just a' (a value of type 'a'). Values of type 'Either a b' contain 'Left b' (usually indicating failure) or 'Right c' (usually indicating success).

<lang Haskell>

validateIBAN :: String -> Either String String

validateIBAN [] = Left "No IBAN number."

else check

where

-- get the country code

country = take 2 normalized

validateIBAN "GB82 WEST 1234 5698 7654 32"

Right "GB82 WEST 1234 5698 7654 32"

 

validateIBAN "GB82 WEST 1234 5698 7654 31"

Left "Invalid IBAN number GB82 WEST 1234 5698 7654 3: Number length does not match."

 

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